1. Field of the Invention
The present invention relates to a solid-state imaging apparatus for imaging a two-dimensional optical image input thereto.
2. Related Background Art
The imaging apparatus employing a solid-state image sensor represented by a charge coupled device ( hereinafter referred to as a CCD ) has been used in various kinds of fields including household videos. However, the CCD has a low charge transfer efficiency. When charges stored in photo diodes occupying comparatively a large light receiving area are handled to be transferred, they are not transferred completely. For such reason, in the specified field, among the solid-state imaging apparatuses, MOS type image sensors have been preferably employed which produce no problem on the charge transfer efficiency.
Among the MOS type image sensors, the ones for imaging two-dimensional optical images have heretofore adopted the system wherein a single discrete amplifier is provided for a photo diode array having a plurality of two-dimensionally arranged photo diodes, a light detection signal is fetched from each photo diode after it has been amplified by the amplifier. Recent years, the proposals to mount both of a reading-out circuit and a light detection circuit on the same chip and to modify a system of circuit structure have been made, in order to increase an S/N ratio for the light detection signal and to miniaturize the apparatus while utilizing the merits of the MOS image sensors.
Such representative example of the proposals is the solid-state imaging apparatus disclosed in Japanese Patent Application Laid Open Heisei 4-3588. FIG. 1 is a circuit diagram of this solid-state imaging apparatus. As shown in FIG. 1, the apparatus comprises (a) a light receiving unit 930 consisting of an N2 number of vertical light receiving sections 920 arranged in a horizontal direction, each of which is connected to common output lines and is provided with an N1 number of light receiving devices 910 arranged in a vertical direction, each of light receiving devices being composed of a photoelectric conversion element 912 and a switching element 912; (b) integration circuits 940, each being arranged for corresponding one of the vertical light receiving sections 920 to integrate the output therefrom and having a charge amplifier 941; (c) sample-and-hold circuits 950, each sampling/holding the signal from corresponding one of the integration circuits 940; (d) switching circuit 960, each controlling the output/non-output of the signal from corresponding one of the sample-and-hold circuits 950 to the outside; (e) a vertical shift-register 971 for instructing to determine the light receiving device 910 to read out the light detection result for the vertical direction; and (f) a horizontal shift-register 972 for instructing to determine the light receiving device 910 to read out the light detection result for the horizontal direction.
With such constitution, a light detection signal in accordance with a light intensity detected by each light receiving device is output through a video signal wiring 980, and the impedance conversion is conducted by buffer circuits 990.